Method and apparatus for drawing sheet glass

ABSTRACT

Method and apparatus for drawing sheet glass, wherein the temperature of the incipient sheet from the line of draw to the drawing rollers is controlled at and along the width of the sheet to effect uniformity of thickness of the sheet throughout its width. Control is effected by establishment of a plurality of series of individual compartments in contiguous side-by-side relation and extending along lines which are generally parallel with the sheet and extend transversely of its length direction, closely adjacent the line of draw. Each series of compartments is allochirally positioned on a respective side of the sheet or line of draw; and each compartment is individually supplied with coolant at an individually controlled rate. By such individual control of the rate of flow of coolant it is assured that the temperature of each section of the sheet, consisting of an increment of length thereof, extending transversely from one side edge of the sheet to the other, is uniform and the temperature differences between one such increment and the next adjacent one are maintained at proper predetermined values. Control of rate of circulation of coolant through the several compartments may be automatic.

United States Patent [72] Inventor Jean Francois Flori Chalon-sur-Saone,France [21 1 Appl. No. 540,696 [221 Filed Apr. 6, 1966 [45] PatentedSept. 21, 1971 [73] Assignee Compagnie de Saint-Gobain Neuilly surSeine, France [32] Priority Apr. 12, 1965 [33] France [31] 12,829

[54] METHOD AND APPARATUS FOR DRAWING SHEET CLASS 15 Claims, 14 DrawingFigs.

[52] US. Cl 65/83,

65/95, 65/194, 65/204, 65/348, 65/356 [51] Int. Cl C03b 15/02 [50] Fieldof Search 65/204, 83,

[56] References Cited UNITED STATES PATENTS 2,519,457 8/1950 Halbach eta1 65/204 X 2,655,765 10/1953 Walters 65/204 X 2,828,948 4/1958Caldwell, Jr. et a1. 65/204 X 3,223,502 12/1965 65/204 X Ward et al.

Primary ExaminerArthur D. Kellogg Att0rneys-Dale A. Bauer, John L.Seymour and Bauer and Seymour ABSTRACT: Method and apparatus for drawingsheet glass, wherein the temperature of the incipient sheet from theline of draw to the drawing rollers is controlled at and along the widthof the sheet to effect uniformity of thickness of the sheet throughoutits width, Control is effected by establishment of a plurality of seriesof individual compartments in contiguous side-by-side relation andextending along lines which are generally parallel with the sheet andextend transversely of its length direction, closely adjacent the lineof draw. Each series of compartments is allochirally positioned on arespective side of the sheet or line of draw; and each compartment isindividually supplied with coolant at an individually controlled rate.By such individual control of the rate of flow of coolant it is assuredthat the temperature of each section of the sheet, consisting of anincrement of length thereof, extending transversely from one side edgeof the sheet to the other, is uniform and the temperature differencesbetween one such increment and the next adjacent one are maintained atproper predetermined values. Control of rate of circulation of coolantthrough the several compartments may be automatic.

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. 3mm JEAN-FRANCOIS FLoru PATENTEDSEP21 l9?! 3.607; 183

SHEEF 5 [IF 5 I v GLASS SHEET MOVING ,1 Vfi/ OUT OFPLANE OF FIGURE -1SCANS GLASS FOR 58 THlCKNESS FIXED TRACK 59 PRESSURE CONTROLoC STANDARD0 REFERENCE W 5 PRESSURE J64 ,FIXED C'OMMUTATOR BAR -ELECTROMAGNETICVALVE COOLANT OUT F|G.l3.

INVENTOR Jean Francois Flori ATTORNEYS METHOD AND APPARATUS FOR DRAWINGSHEET GLASS This invention relates to the fabrication of sheets ofthermoplastic materials by drawing and, in particular is concerned withthe production of glass in sheet form by vertical drawing fr' .1 a bathof molten glass.

In this fabrication the molten glass as it is drawn from the bath by themachine, is rapidly cooled by heat exchange means disposed at each sideof the incipient ribbon. Such cooling is necessary in order to bring theglass to a physical state such that it may be gripped without damage,between the rolls of the drawing apparatus. During its passage throughthe drawing shaft or chamber the glass is annealed by gradually loweringits temperature at a controlled rate. This annealing is necessary inorder to avoid the development of excessive internal stresses within theglass.

Control and regulation of temperature and rate of cooling is necessaryat every stage of production, in order to obtain properly annealedsheets of good quality and uniform desired thickness.

Defects due to variations in thickness of the sheet are caused largelybe variations in temperature of the glass at the moment of formation ofthe ribbon, that is, at the location where molten glass at the foot ofthe ribbon, curves upwardly with decreasing thickness to form anincipient ribbon.

in order to avoid warping of the ribbon longitudinally as well astransversely during its formation as it moves in and along the drawingshaft, it is necessary that the temperature of each face thereof besubstantially uniform at all points in each respective line extendingtransversely of the sheet, and that the temperature of each face of thesheet along corresponding or directly opposite lines, be the same. Alsothe temperature gradient between successive transverse lines should besmooth and even.

The various prior art means devised for obviating defective sheet glasseither are not effective or have disadvantages which render themcommercially impracticable.

in one such means there are provided metal screens called pads, ofappropriate dimensions and disposed at judiciously selected locations,in order to cool the ribbon during drawing. This arrangement, while itenables the attenuation or reduction to a certain extent, of theaforesaid undesired heterogeneity of temperature, nevertheless hasdisadvantages. The emplacement of these screens must be effectedmanually after opening of access doors in the walls of the drawingapparatus. Since the interior of the drawing shaft is at a pressurebelow atmospheric, opening of such doors creates a rush of cooler airinto the shaft and creates undesired and undesirable temperaturevariations therein. Furthermore, in the course of time, these screens orpads become encrusted or coated with oxidations, deposits of dust,sulfates, etc., which create variations in rates of heat exchangebetween the screens and the glass. In addition the action of the screensis not uniform or continuous over the areas of the glass to be cooled,and their utilization is not sufficiently flexible to effect precise andcontinuous control of thickness because in order to change or modifytheir action it is necessary to change them or to vary their locationsor positions of adjustment.

In another prior art device it has been proposed to provide auxiliarycooling means which are mobile and can thus be moved about from place toplace within the apparatus, to correspondingly vary the geometricalrelations of the several cooling means and their heat exchange rateswith the glass. But the introduction of such mobile auxiliary coolingmeans into the drawing apparatus, in turn, presents disadvantagesbecause these means perturb and alter the paths of gaseous currentswithin the apparatus and thus unavoidably act, to themselves createinequalities in temperature at various locations therewithin.

In still another proposed prior art arrangement, cooled or heated gas,in particular derived from burners disposed within the drawingapparatus, is discharged and directed to form gaseous currents moving indesired appropriate paths. Such arrangements have the drawbacks that thepaths of the currents created within the apparatus are not preciselycontrollable. Furthermore, control of these currents is a delicateoperation requiring great skill, so that constant and continuous properregulation thereof is practically impossible.

The employment of heat radiators has been suggested. But .this procedureis directly contrary to the desired aim, which is to cool the glass, notto heat it, and requires the use of devices at a temperature higher thanthat of the glass. Such devices are expensive and theiruse involves alarge and costly expenditure of energy.

' The present invention has for its chief objectthe provision of animproved method and apparatus for the fabrication of sheets ofthermoplastic materials, especially glass, by drawing means whicheliminate drawbacks of prior art procedures and apparatuses, and enableprecise and accurate regulation and control of the cooling of thematerial with the resulting production of a ribbon of uniform desiredthickness, of excellent quality, and devoid of defects.

In accordance with the foregoing chief object it is a further object toeffect the desired heat exchange by radiation between the glass and thecooling means.

Ancillary to the foregoing objects, it is another object to provide anapparatus which assures that every point of each respective line lyingin the surface of the ribbon and normal to its direction of travel, willbe at the same temperature, that the temperatures of each pair of linesof respective surfaces of the ribbon and located horizontally oppositeone another, will be at the same temperature, and that the temperaturegradient between successive or contiguous lines will be gradual andsmooth.

Yet another object is to provide an apparatus as aforesaid, by whichchanges in temperatures to effect the desired uniformity, may bemanually or automatically controlled in a relatively simple andeffective way.

A still further object is to provide a method and apparatus for theproduction of sheet material, particularly glass, which by reason of thesuperior product produced, of uniform thickness, reduces losses andcosts per unit length of material.

Other objects and advantages of the invention will become clear to thoseskilled in the art, after a study of the following detailed disclosure.

I have found that the rate of heat exchange between the surface of astandard cooling means and the glass, remains practically constant whenthe surface temperature of the means remains less than about 0.3 that ofthe glass subject to the cooling action thereof.

On the other hand, when the temperature of the surface of the cooler isgreater than 0.3 that of the glass, the rate of heat exchange variesrapidly with changes in the ratio. These variations become increasinglyimportant as the temperature of the cooling means approaches that of theglass. Of course, the absolute value of heat exchange per unit areadecreases as the temperature of the surface of the cooler approachesthat of the glass.

According to one feature of the invention there is disposed in proximityto the glass, parallel with its surface, a plurality of surface elementslocated in side-by-side relation and positioned transversely to thedirection in which the glass is drawn. These elements are able to effectheat exchange with the glass by radiation so that it is thus possible tocontrol the cooling or rate of heat exchange at each location along thesurface of the incipient sheet, by individually and independentlycontrolling the temperature of each of these elements.

In accordance with an important feature of the invention, the surfacetemperature of each of the aforesaid elements is kept at a value suchthat the ratio is greater than 0.3 that of the surface of the glass atthe area of exchange.

In a first embodiment for carrying out the inventive method, the coolingmeans comprises individual juxtaposed elements. in a second embodimentthe cooling means comprises a common cover'with areas or spots along thelength thereof which may be individually kept, each at a selectedtemperature different from the others, in order to enable a. desiredrate of heat exchange at each area. Since there is an exchange of heatby conduction along the wall or cover from one area to the next adjacentareas, deleterious effects on the cooling of the glass otherwise causedby abrupt variations in temperature between any one area and the nextcontiguous areas, are avoided.

The cooling elements may be tubes disposed one after the other througheach of which there is impelled a coolant having a sufficiently highboiling point. Such coolants should have a high thermal capacity and, inparticular, may be one of the organic substantially nonflammable liquidspresently used in industry for heat exchange purposes. It is alsopossible to use gas, in particular, air.

In another embodiment the cooling elements are so formed that there is atemperature gradient between the external and internal wall surfacesthereof. A coolant having a relatively low boiling point, such as water,for example, may be used. For this purpose the cooling element, at leastthat portion thereof adjacent the glass, is of a material having arelatively low heat conductivity, such as various cements or plasticmaterial which maintains sufficient strength and solidity attemperatures around 350 C. One such material is known by the trade nameof Teflon. The thickness of the wall formed by the material selected isso chosen that the desired temperature gradient will be established andmaintained. The cooling element may also be made of metal forming doublewalls which form between them a dead air space to effect the desiredreduced rate of heat transmission. Or the space between the walls may befilled with a material such as powder of relatively low heatconductivity.

In one construction of the cooling element, a series of tubes arejuxtaposed in parallel relation and spaced in the direction transverselyof the direction of drawing of the glass. These tubes are cooled uponthe side opposite to that facing the glass, by a chilled fluid. Thedimensions of these tubes, the thickness of their walls, and thematerial of which they are made, are so selected that when no fluid iscirculating through them, the heat exchange by conduction between thetwo walls, through the partition, results in a temperature of theexternal wall slightly higher than the desired operating temperature.Thus the temperature of the external walls of the tubes may be regulatedwith great precision by the circulation of coolant through the interiorof the double walls, about the partition. This coolant may, for example,be air having a temperature such that its circulation will, byconvection, lower the temperature of the external walls to the desiredvalue.

The drawing shows several nonlimiting examples of apparatuses by whichthe method may be carried into practice.

In the drawing:

FIG. 1 is a diagram showing a curve of relative heat exchange rates byradiation;

FIG. 2 illustrates schematically in transverse vertical section, aglass-drawing machine of the Pennvernon-type, equipped with means forcarrying the inventive method into practice;

FIG. 3 is a longitudinal sectional detail view showing a portion of acooling tube, the internal arrangement of partitions and means forfeeding coolant to, and exhausting the same from, the tube;

FIG. 4 is a section take in a plane identified by line 4-4, FIG. 3;

FIG. 5 is a schematic vertical section transversely of the sheet,showing a modification;

FIG. 6 is a vertical longitudinal section to an enlarged scale, of theheat exchange element used in the modification of FIG. 5, with outertube omitted for greater clarity of illustration;

FIG. 6a is a transverse section with outer tube present, and taken in aplane identified by line 6a6a, FIG. 6;

FIG. 7 is a detail plan view looking from below, showing the staggeredor offset relation between the effective cooling sections of twocontiguous pipes of the construction depicted upon FIG. 6;

FIG. 8 is an elevational view of a third modification of heat exchangeelement in which there are formed aligned individual heat exchange unitsin side-by-side transversely aligned relation;

FIG. 9 is a sectional view taken in a plane identified by line 9--9,FIG. 8, looking in the direction of the arrows;

FIG. 10 is a transverse sectional detail view showing still another formwhich the cooling element may have;

FIG. II is an elevational view looking from right to left, FIG. 10;

FIG. 12 is a perspective view showing details of construction of theassembled apparatus; and

FIG. 13 is a schematic view showing a form of apparatus forautomatically controlling the flow of coolant through the severaldiscrete cooling chambers.

FIG. 1 shows a curve representing the variations in heat exchange byradiation, between two spaced surfaces at the respective temperatures oft and T. In this curve, abscissas are in terms of the ratios t/T andordinates l-t/T']. Inspection of the curve shows that for values of t/ Tup to about 0.3, the corresponding values of l t "T] change very little.For example, at ratio t/T=O.3, the corresponding ordinate value which isunity for t/T=0, is still 0.9919. On the other hand, the decrease inordinate values becomes vary rapid with values of t/T above 0.3.

It is clear that for efficient regulation of cooling of the surface ofthe glass, it is advantageous that the cooling elements be maintained attemperatures which will be greater than 0.3 that of the glass. Forinstance, when the temperature I of the cooling surface is kept below0.3 that of the glass, a substantial change in t does not materiallyalter the rate of heat transmission per unit area, by radiation fromglass to cooling surface. On the other hand, when t is maintained at avalue such that the ratio is above 0.3, slight changes in 2 result incorrespondingly large changes in rate of heat transmission.

Upon FIG. 2, l have depicted schematically a glass-drawing machine ofthe so-called Pennvernon-type. However, this is by way of example only;and it will be well understood by those skilled in the art, that themethod and apparatus are easily adapted for use with other types ofglass-drawing machines such as the Fourcault, Colburn, and others.

In the apparatus shown, the ribbon of glass 1 is drawn vertically fromthe surface of the bath of molten glass 2. The usual drawing bar or boat3, submerged in the bath, assists in causing the incipient ribbon toform into a foot 4 which, as the glass moves upwardly, thins into sheetform for passage between pairs of vertically spaced drawing rolls 5located in tower or shaft 6. As the incipient sheet moves upwardly at 4from the surface of the bath, it passes between coolers 7, as is wellknown in the art.

The temperature of the glass at the location where the ribbon is formed,should be uniform from point to point along lines in the surface of theglass normal to the plane of FIG. 2. In the prior art this uniformity isnot attainable in practice, so that the temperature of the glass atsuccessive points along any given line, as aforesaid, varies from pointto point where the foot 4 gradually contracts in thickness to formribbon 1. This lack of uniformity of temperature causes a like variationin viscosity of the glass, with the result that the thickness of thedrawn sheet or ribbon correspondingly varies from place to place.

In addition to the usual cooling means 7, previously mentioned, Iprovide auxiliary cooling means which upon FIG. 2 are identified as apair of tubes 8 each located below and suspended by suitable means froma respective one of conventional coolers 7.

FIGS. 3 and 41 show in vertical longitudinal and transverse section andto an enlarged scale, the construction of one of these tubes 8. Eachtube which, as shown upon FIG. 2, is located closely adjacent the footof the incipient ribbon, is divided into lower and upper chambers 10 and11, by a wall 9 secured in and extending horizontally and diametricallyof the tube. Lower chamber 10, in turn, is divided into compartmentssuch as 12, by semicircular partitions 13 fixed at spaced intervals inand along the chamber. Wall 9 is apertured as indicated at so that thereis at least one opening for the exhaust of cooling fluid from itscompartment. In the model shown there are two of these openingssymmetrically located upon opposite sides of a coolant supply pipe 14.

There is one supply pipe 14 for each compartment. Referring moreparticularly to FIG. 3, each pipe 14 descends vertically from one of thecoolers 7, passes in sealed relation through a respective on of a numberof holes in the top of conduit 8, and another hole in wall 9, and hasits lower end terminating centrally within a respective one of thecompartments.

In operation, cooling fluid or gas such as air, is impelled downwardlythrough each tube 14, enters its respective compartment 12 where heatexchange by radiation takes place between the molten glass 2 and theexterior walls of each compartment 12. The fluid then passes throughaperture 15 and is exhausted from upper chamber 11 and recirculated tomeans whereby it is recooled.

Thus by regulating the amount or rate of flow of coolant to each of thecompartments 12, individually as by means of valves not shown, one ineach pipe 14, a very close and precise control is afforded, of thetemperature of the glass adjacent each location opposite each of thecomparments 12. This is clear from inspection of FIGS. 3 and 4; and anyundesired and undesirable temperature differences between contiguousareas in the surface of the glass may be corrected and the incipientsheet maintained at the desired uniform temperature gradient in thedirection of its length. The distance between successive partitions l3depends, of course, on the precision of temperature control required ordesired. In most installations a distance of two centimeters enables atemperature control sufficient to avoid differences in thickness of theribbon which are otherwise unavoidably caused by temperature variationsof the glass at and adjacent foot 4 of the incipient sheet or ribbon,and result in imperfections in the finished product.

FIGS. 5 through 7 show a second form which the auxiliary cooling meansmay have. In this construction, referring especially to FIG. 5, ribbon1, bath of molten glass 2, drawing boat 3, foot 4, and coolers 7, are aspreviously described in connection with FIG. 2. At 44 there isidentified a metal tube which extends horizontally over the surface ofthe molten glass and at one side of the cooler 7. While in FIG. 5 onlyone tube 44 is shown, it will be understood that a second andidentically constructed auxiliary cooler is allochirally disposedadjacent the right-hand cooler 7, as viewed in this figure.

A group or bundle of small pipes 40 is disposed within tube 44 in spacedparallel relation as shown upon FIG. 6a. Heat insulating material 41 mayfill the interstices between pipes 40, within tube 44.

Each pipe 40 includes a U-shaped depending bend whose sides passdownwardly through a respective pair of apertures in the lower wall oftube 44. Thus, referring the FIGS. 6 and 6a, one of these bends isindicated at 40a and from this it is noted that the bight portion of thebend is parallel with and closely adjacent the surface of the moltenglass. See also FIG. 5. As is shown by these figures, each tube has butone bend. The bights of all bends lie in a common plane parallel withthe surface of the glass, but are offset with about a 50 percent overlapin this plane and in a direction parallel with ribbon 1. The arrangementof bights of the tubes is well shown upon FIG. 7 from which it is seenthat these form two rows 42 and 43 closely spaced and parallel with thesurface of the molten glass. Each row comprises a series of bights incontiguous endto-end aligned relation.

Thus by manipulation of valves 46, FIG. 6, one in each pipe, exteriorlyof the melting tank 47, the amount or rate of flow of coolant passingthrough each of the pipes may be varied to ef feet a precise control ofthe surfaces of the glass near the foot Each bight of the tubes may haveits upper surface covered with shield of heat insulation such asindicated at 45. This directs the cooling effect downwardly and promotesefficient is divided into discrete chambers 16, by partitions 48.

uniformly spaced therealong, so that each chamber may be separately andindividually supplied with coolant by a respective one of a plurality ofinlet pipes 17. As clearly shown, each inlet pipe has a valve 18 locatedexteriorly of the cooler. Fluid is exhausted from each chamber through arespective one of a plurality of pipes 19. FIG. 9 shows thatcompartments 16 are positioned in contiguous side-by-side relation toform a row extending completely across the ribbon, at a location closelyadjacent the location where it moves upwardly. As in forms of theinvention previously described, the coolant may be air; and bymanipulation of valves 18 the amount of fluid impelled through eachchamber 16 is varied to effect a precise and exact control oftemperature at the surfaces of the glass.

The ribbon of glass is thus formed by rapidly lowering its temperaturefrom about l000 C. adjacent foot 4, to its solidification temperaturewhich, in general, is about 800 C. The conditions of cooling determinethe thickness of the sheet produced.

As shown upon FIG. 2, in order to compensate for variations in thicknessit is also desirable to regulate the temperature of coolers 7, at leastover the lower parts 7a thereof, effective upon zone a" of the glass.Since the upper part of the coolers act solely to rapidly lower thetemperature of the glass to, say, about 500 C., so that the glass is notdamaged by passage between the drawing rolls of the machine, it is notessential as a rule, to closely regulate the temperature in this zone,transversely of the sheet. However, it is advantageous to maintain thetemperature of the cooler sufficiently high to avoid deposits orencrustations which would otherwise form thereon.

The separation of the lower portion of the cooler into discretetemperature zones may be effected by any of the means previouslydescribed. This separation may be effected in a particularly efficientand commercially satisfactory way, by continuous conduits defined bydouble walls at the base of the cooler, and impelling through each acurrent of fluid whose temperature can be controlled individually foreach conduit. Such control is readily effected by means of pipes 19,each having a valve 20 therein and each leading to a respective one ofthe chambers. As shown upon FIG. 2, these pipes may be connected with asingle heat exchanger 21 and which may also serve as the supply of fluidfor the upper portion or chamber of coolers 7.

After the glass has been formed into a ribbon, it moves into the drawingshaft 6 where it is annealed. It is important, at the moment that eachincrement of length of the ribbon moves into the shaft, that it be ofuniform temperature transversely of the sheet and that both surfacesthereof be at the same tem perature. If such conditions do not exist,the ribbon tends to warp or distort and this may cause breakage of theglass when it enters between drawing rolls 5.

In order to avoid any such differences of temperature, auxiliary coolers22 are disposed upon and adjacent respective surfaces of the ribbon atthe location where it enters the shaft. These auxiliary coolers may beformed like coolers 8 previously described in connection with FIGS. 3and 4. However, other embodiments such as those depicted upon FIGS. 10and l 1 may be used with equally satisfactory results.

Referring to the latter figures, each cooler 22 is shown as rectangularin transverse vertical section. The interior thereof is divided into,chambers 48,49 by a vertical partition 23 extending transversely in andalong the cooler. Chamber 48 is, in

" turn, divided by vertical, laterally and uniformly spaced partitions24, into a number of discrete compartments 25. Each of thesecompartments is individually supplied with coolant through a commonconduit 26 having branches 27 each leading to a respective one ofcompartments 25. A control valve 28 is included in each branch 27. Thecoolers 22 are disposed, one on each side of the ribbon and are soregulated that when the sheet passes into the drawing shaft, thetemperature of each increment of length, forming a narrow striptransversely across the sheet, is the same throughout the length of thestrip, and both faces of the strip are at the same temperature.

At the location where it enters the drawing chamber or shaft, the glassis at a temperature of about 500 C. In conformity with the invention,auxiliary coolers 22 will thus have a temperature of the order of 150 to200 C. However, it is desirable that the surface temperature of thesecoolers be somewhat above the optimum value, say 350 C., in order toprevent the formation of deposits or encrustations upon the surfacesthereof.

After it enters the drawing shaft, the glass is progressively cooled toa temperature at which it may be cut into sections. Regulation of therate of cooling is important because it determines the annealing andquality of the glass. In conformity with the invention, auxiliarycoolers identified at 29, FIG. 2, are located within shaft 6, as shown,in order to regulate the rate of cooling of the ribbon as it passesupwardly therealong, and thus assure proper annealing. Otherwisevariations in such rate will occur because of convection currents withinthe shaft.

FIG. 12 shows a variation of the cooling means, and which is used toassure regulation of temperature of each point of the surface of theglass at the moment of its formation, the location where it enters thedrawing shaft, and/or within the shaft. These cooling means comprise afirst U-shaped chamber 31 disposed perpendicularly to the surface of theglass, and a second U-shaped chamber 32 fitting within and in contactwith the first. The exterior chamber is supplied with a fluid such asair, through a header 33 and pipe 51 having valve 34 therein. The secondor interior chamber 32 is supplied with coolant such as water, through aheader 35 and branch pipe 52 which may also have a valve therein, notshown. Fluid is withdrawn from chambers 31 and 32 through pipes 53 and54, respectively. It will be understood that, as in the embodimentspreviously described, for example in connection with FIGS. 8 and 9,there are a multiplicity of these assemblies 31, 32, in contiguousside-by-side relation and extending transversely across and adjacent theglass. Each group of chambers 31 may be supplied from header 33 and eachgroup 32 from header 35. The entire assembly is supported by a beam 36supported at its ends and extending horizontally and transversely acrossthe apparatus. FIG. 2 shows that header 33 is supplied with air from ablower 36. Exhaust pipes 53, FIG. 12, connect with a header 55, FIG. 2,by which air is returned to a cooler or heat exchanger, not shown, andthence returned to the blower for recirculation.

Automatic control of the temperature of the several chambers to maintainthe uniformity of temperature as previously described, may be effectedby an apparatus such as the one shown upon FIG. 13 operating on theprinciple of X-ray absorption or optical interference. Referring to thisfigure, 1 represents to a greatly enlarged scale, a portion of a ribbonof glass being drawn upwardly out of the plane of the figure. A track 56is fixed horizontally, parallel with and extending across ribbon 1. Thetrack mounts, for guided translation along it, an assembly generallyidentified at 57, comprising means 58 for detecting changes inthickness, from a predetermined desired value, of the ribbon at eachlocation scanned. By means of this apparatus the thickness of the sheetis tested or explored at each location. Testing every few hours issufficient because in practice, the thickness varies very little fromhour to hour. Measurements may be taken every cm., or less if necessary.There are thus provided L/IO electrical indications every few hours, Lbeing the width of the sheet in centimeters.

These indications or measurements of thickness are sequential effectiveupon a recording transmitter 59 which converts each indication insequence, into a corresponding proportional value of pneumatic pressure.A pressure-responsive device 60 consists of a closed casing divided intotwo discrete chambers by a bellows or diaphragm 61. One of thesechambers is connected as at 62 with a source of pressure corresponding,to a predetermined scale, with the desired thickness of the glass. Theother chamber is connected as by conduit 63, with the aforesaidrecording transmitter. Thus, when the instrument detects at variation ofthickness of the sheet at any given location, from that desired, thediaphragm or bellows 61 is flexed to close one or the other of twocircuits 64 or 65 and which reversely control a servomotor. There is oneservomotor for each respective valve such as 18, 20, 28, 34, etc. Whenthe servomotor is energized by deflection of the diaphragm, to operatein one direction, its valve such as 18', is closed to decrease the rateof flow of coolant to the corresponding compartment. When energized tooperate in the other direction, by opposite deflection of the diaphragm,its valve is opened to increase the rate of flow of coolant to thatchamber.

By means of a commutator device generally identified at 66 andcomprising a contact 67 fixed with assembly 57 to move in synchronismwith movement of the measuring instrument, the pressure responsivedevice is connected sequentially with each servomotor. Thus when anexcessive thickness is detected at any point or location adjacent thepath of the instrument, the resulting pressure differential effectiveupon diaphragm 61, closes a corresponding to one of the aforesaidcircuits which operates the valve such as 18' controlling flow ofcoolant to the corresponding chamber such as 16, to decrease the rate offlow sufficiently to increase the temperature at that point or locationand thus decrease the thickness thereat to normal or desired value. Onthe other hand, when the thickness measured at a given point is toosmall, the effect upon the diaphragm device closes the second contactand thus effects rotation of the servomotor to which it is at that timeconnected, to decrease the rate of flow of coolant to the chamber atthat location. Thereby the temperature at that point or locationincreases and the thickness of the sheet thereat is correspondinglydecreased. In the figure, valves 18', inlet pipes 17 and coolingcompartments 16 may be the same as depicted upon FIGS. 8 and 9, it beingunderstood that the same type of automatic control as just described, isequally adaptable to the species of FIGS. 3, 4; 5, 6, etc., and alsothat, as in FIG. 9, the cooling compartments are in a row extendingcontinuously along and adjacent the line of draw, with each segment ofcommutator bar 68 in registration with and extending over the samedistance, parallel with the track 56, as its corresponding compartment16.

Numerous modifications, substitutions of equivalents, alterations andchanges in relative positions and shapes, will readily occurto thoseskilled in the art, after a study of the foregoing disclosure. Hence thedisclosure should be taken in an illustrative rather than a limitingsense.

In the claims the expression line of draw" has the usual meaning in theart, such as, referring to FIG. 2, a line defined by the intersection ofthe plane of ribbon l, with a plane lying in the surface of the bath ofmolten glass 2.

Having fully disclosed the invention, what I claim and desire to secureby US. Letters Patent is:

l. The method of drawing sheet glass in a fixed vertical direction froma molten bath, comprising, establishing a first plurality of fluidchambers in contiguous, side-by-side relation along a first lineparallel with the incipient sheet at one side thereof, normal to saiddirection, and extending completely and without hiatus across the sheet,for direct heat exchange with and adjacent the incipient sheet,supplying cooling fluid for the incipient sheet to each said chamber,and individually controlling the flow of fluid to each said chamber, tothereby maintain constant the surface temperature of the sheet adjacentsaid first line.

2. The method of claim 1, and maintaining the effective temperature ofthe cooling fluid at not less than about 0.3 of the temperature,measured on the Centigrade scale, of the glass at the location of heatexchange with said fluid.

3. The method of claim 1, establishing a second plurality of fluidchambers in contiguous side-by side relation along a set and lineparallel with said first line and adjacent the incipient sheet at theother side thereof, normal to said direction, and extending completelyand without hiatus across the sheet, for direct heat exchange with andadjacent the incipient sheet, supplying cooling fluid for the incipientsheet to each said chamber of said second plurality, and individuallycontrolling the flow of fluid to each said chamber of said secondplurality, to maintain constant the surface temperature of the incipientsheet adjacent said second line.

4. The method of drawing sheet glass in a fixed vertical direction froma bath of molten glass, comprising simultaneously flowing cooling fluidinto heat exchange contact with a first plurality of discrete surfaceseach in direct heat exchange relation with and adjacent the incipientsheet being drawn upwardly from the bath, and extending continuously andwithout hiatus in a line parallel with the sheet, normal to saiddirection, entirely across the sheet, and individually and selectivelyflowing cooling fluid into heat exchange contact with all or selectedones only of said surfaces, to maintain constant the temperature of thesheet adjacent to and along said line.

5. In a process of drawing glass sheet in which the sheet is drawnupwardly from the surface of a bath of molten glass, along a line ofdraw lying essentially in the surface of the bath, and progressivelycooled to solidification, the step which comprises equalizing thetemperature of the glass, in a region where the glass is still plastic,by separately and individually cooling discrete areas of the incipientsheet, said areas extending continuously and without hiatus adjacent andalong a line in and transversely of the incipient sheet and parallelwith, adjacent and essentially coextensive with said line of draw.

6. In apparatus for drawing sheet glass, a melting tank, means operableto draw glass from said tank in a fixed upward direction and to form thesame into a ribbon of essentially uniform thickness and width, firstcooler means comprising a continuous, uninterrupted first surfaceextending parallel to and adjacent the line of draw of the ribbon, firstpartition means connected with said first surface and forming therewitha first multiplicity of closed, discrete, heat exchange compartmentsextending in side-by-side relation adjacent and along the line of drawand adjacent to the incipient ribbon being drawn upwardly from the tank,said compartments forming a first row parallel with said line of drawand normal to said direction, first conduit means for supplying andexhausting cooling fluid independently to and from each saidcompartment, for direct heat exchange contact with the correspondingportion of said first surface, and for direct heat exchange with andadjacent the incipient ribbon being drawn upwardly from the bath ofmolten glass in said tank, and means operable to selectively andindependently control the flow of cooling fluid into and from each saidcompartment of said first multiplicity.

7. The apparatus of claim 6, said first surface lying essentially in aplane parallel with the surface of molten glass in said tank.

8. The apparatus of claim 6, said direction being vertical, secondcooler means comprising a continuous, uninterrupted second surfaceextending parallel to and adjacent the line of draw of the ribbon, andon the side thereof opposite to said first surface, second partitionmeans connected with said second surface and forming therewith a secondmultiplicity of closed, discrete, heat exchange compartments extendingin side-by-side relation along said line of draw, said secondmultiplicity of compartments conjointly forming a second row parallelwith said line of draw and normal to said direction, second conduitmeans for supplying and exhausting cooling fluid independently to andfrom each said compartment of said second multiplicity, for direct heatexchange contact with the corresponding portion of said second surface,and means operable to selectively and independently control the flow ofcooling fluid into and from each compartment of said secondmultiplicity.

9. The apparatus of claim 6, said surface of said first cooler meanscomprising a main pipe, a wall in said main pipe extending thereacrossand longitudinally therealong, to form with the walls of said main pipe,first and second discrete chambers, said first partitionmeans'comprising partitions in and spaced along said second chamber,anddividing the same into said first multiplicity of discretecompartments, said wall having a multiplicity of apertures each openinginto a respective one of said compartments, said first conduit meanscomprising a multiplicity of cooling fluid supply pipes each incommunication with a respective one of said apertures.

10. The apparatus of claim 9, said main pipe being disposed to extendadjacent, and parallel with the line of draw, the wall portion of saidmain pipe, forming said second chamber, confronting the surface of thebath of glass in said tank.

11. The apparatus of claim 6, said first cooler means comprising aclosed essentially parallelepipedal casing having its longitudinal axisadjacent and parallel with said line of draw, said casing comprising abottom wall essentially parallel with the surface of molten glass insaid tank, and a vertical sidewall parallel with the plane of the ribbonbeing drawn, an auxiliary partition in said casing generally parallelwith and spaced above said bottom wall and dividing the interior of saidcasing into lower and upper chambers, said first partition meanscomprising a multiplicity of spaced partitions in said lower chamberand, in conjunction with the corresponding portions of said bottom andvertical sidewalls, dividing said lower chamber into sequential discretecompartments in side-byside contiguous relation, to define a rowparallel with and adjacent said line of draw, said first conduit meanscomprising a multiplicity of first supply pipes each opening into arespective one of said compartments, a multiplicity of first exhaustpipes each leading from a respective one of said compartments, a secondsupply pipe and a second exhaust pipe, each opening into said upperchamber, coolant supply means feeding all said supply pipes, and meansin said first supply pipes and operable to individually control the rateof flow of coolant to each said compartment, said upper chamber formingthe principal cooler for the ribbon being drawn.

12. The apparatus of claim 11, all said first supply and exhaust pipespassing through said upper chamber and opening into said lower chamberthrough respective apertures in said auxiliary partition.

13. The apparatus of claim 6, said first cooler means comprising acoolant tube extending parallel with the line of draw, a multiplicity ofpipes mounted within said tube, in parallel relation therein, each saidpipe including a U-shaped bend, the sides of each bend extending througha respective pair of apertures in said tube, to position the bightthereof exteriorly of the tube, all said bights being essentiallycoplanar in a plane parallel with the surface of the molten glass insaid tank, each said bight being longitudinally offset from and inoverlapping side-by-side relation with the next adjacent bight,transversely of the ribbon, all said bights conjointly forming a rowextending parallel with and adjacent the line of draw, and substantiallycoextensive with the width of the ribbon, said flow control meanscomprising a multiplicity of valves, each in a respective one of saidpipes.

14. The apparatus of claim 6, said first cooler means comprising a firstmultiplicity of discrete U-shaped chambers, means mounting said chambersin side-by-side contiguous relation, each in a respective one of amultiplicity of parallel planes normal to the line of draw, to form arow extending parallel with and adjacent said line of draw andessentially coextensive therewith, said first conduit means comprising afirst header and a multiplicity of first pipes each connecting saidfirst header with a respective one of said chambers, a multiplicity ofvalves each in a respective one of said first pipes, and means forexhausting fluid from each chamber of said first multiplicity.

pipes each connecting said second header with a respective one of saidsecond multiplicity of chambers, and means for exhausting fluid fromeach of said second multiplicity of chambers.

2. The method of claim 1, and maintaining the effective temperature ofthe cooling fluid at not less than about 0.3 of the teMperature,measured on the Centigrade scale, of the glass at the location of heatexchange with said fluid.
 3. The method of claim 1, establishing asecond plurality of fluid chambers in contiguous side-by-side relationalong a second line parallel with said first line and adjacent theincipient sheet at the other side thereof, normal to said direction, andextending completely and without hiatus across the sheet, for directheat exchange with and adjacent the incipient sheet, supplying coolingfluid for the incipient sheet to each said chamber of said secondplurality, and individually controlling the flow of fluid to each saidchamber of said second plurality, to maintain constant the surfacetemperature of the incipient sheet adjacent said second line.
 4. Themethod of drawing sheet glass in a fixed vertical direction from a bathof molten glass, comprising simultaneously flowing cooling fluid intoheat exchange contact with a first plurality of discrete surfaces eachin direct heat exchange relation with and adjacent the incipient sheetbeing drawn upwardly from the bath, and extending continuously andwithout hiatus in a line parallel with the sheet, normal to saiddirection, entirely across the sheet, and individually and selectivelyflowing cooling fluid into heat exchange contact with all or selectedones only of said surfaces, to maintain constant the temperature of thesheet adjacent to and along said line.
 5. In a process of drawing glasssheet in which the sheet is drawn upwardly from the surface of a bath ofmolten glass, along a line of draw lying essentially in the surface ofthe bath, and progressively cooled to solidification, the step whichcomprises equalizing the temperature of the glass, in a region where theglass is still plastic, by separately and individually cooling discreteareas of the incipient sheet, said areas extending continuously andwithout hiatus adjacent and along a line in and transversely of theincipient sheet and parallel with, adjacent and essentially coextensivewith said line of draw.
 6. In apparatus for drawing sheet glass, amelting tank, means operable to draw glass from said tank in a fixedupward direction and to form the same into a ribbon of essentiallyuniform thickness and width, first cooler means comprising a continuous,uninterrupted first surface extending parallel to and adjacent the lineof draw of the ribbon, first partition means connected with said firstsurface and forming therewith a first multiplicity of closed, discrete,heat exchange compartments extending in side-by-side relation adjacentand along the line of draw and adjacent to the incipient ribbon beingdrawn upwardly from the tank, said compartments forming a first rowparallel with said line of draw and normal to said direction, firstconduit means for supplying and exhausting cooling fluid independentlyto and from each said compartment, for direct heat exchange contact withthe corresponding portion of said first surface, and for direct heatexchange with and adjacent the incipient ribbon being drawn upwardlyfrom the bath of molten glass in said tank, and means operable toselectively and independently control the flow of cooling fluid into andfrom each said compartment of said first multiplicity.
 7. The apparatusof claim 6, said first surface lying essentially in a plane parallelwith the surface of molten glass in said tank.
 8. The apparatus of claim6, said direction being vertical, second cooler means comprising acontinuous, uninterrupted second surface extending parallel to andadjacent the line of draw of the ribbon, and on the side thereofopposite to said first surface, second partition means connected withsaid second surface and forming therewith a second multiplicity ofclosed, discrete, heat exchange compartments extending in side-by-siderelation along said line of draw, said second multiplicity ofcompartments conjointly forming a second row parallel with said line ofdraw and normal to said direction, second conDuit means for supplyingand exhausting cooling fluid independently to and from each saidcompartment of said second multiplicity, for direct heat exchangecontact with the corresponding portion of said second surface, and meansoperable to selectively and independently control the flow of coolingfluid into and from each compartment of said second multiplicity.
 9. Theapparatus of claim 6, said surface of said first cooler means comprisinga main pipe, a wall in said main pipe extending thereacross andlongitudinally therealong, to form with the walls of said main pipe,first and second discrete chambers, said first partition meanscomprising partitions in and spaced along said second chamber, anddividing the same into said first multiplicity of discrete compartments,said wall having a multiplicity of apertures each opening into arespective one of said compartments, said first conduit means comprisinga multiplicity of cooling fluid supply pipes each in communication witha respective one of said apertures.
 10. The apparatus of claim 9, saidmain pipe being disposed to extend adjacent, and parallel with the lineof draw, the wall portion of said main pipe, forming said secondchamber, confronting the surface of the bath of glass in said tank. 11.The apparatus of claim 6, said first cooler means comprising a closedessentially parallelepipedal casing having its longitudinal axisadjacent and parallel with said line of draw, said casing comprising abottom wall essentially parallel with the surface of molten glass insaid tank, and a vertical sidewall parallel with the plane of the ribbonbeing drawn, an auxiliary partition in said casing generally parallelwith and spaced above said bottom wall and dividing the interior of saidcasing into lower and upper chambers, said first partition meanscomprising a multiplicity of spaced partitions in said lower chamberand, in conjunction with the corresponding portions of said bottom andvertical sidewalls, dividing said lower chamber into sequential discretecompartments in side-by-side contiguous relation, to define a rowparallel with and adjacent said line of draw, said first conduit meanscomprising a multiplicity of first supply pipes each opening into arespective one of said compartments, a multiplicity of first exhaustpipes each leading from a respective one of said compartments, a secondsupply pipe and a second exhaust pipe, each opening into said upperchamber, coolant supply means feeding all said supply pipes, and meansin said first supply pipes and operable to individually control the rateof flow of coolant to each said compartment, said upper chamber formingthe principal cooler for the ribbon being drawn.
 12. The apparatus ofclaim 11, all said first supply and exhaust pipes passing through saidupper chamber and opening into said lower chamber through respectiveapertures in said auxiliary partition.
 13. The apparatus of claim 6,said first cooler means comprising a coolant tube extending parallelwith the line of draw, a multiplicity of pipes mounted within said tube,in parallel relation therein, each said pipe including a U-shaped bend,the sides of each bend extending through a respective pair of aperturesin said tube, to position the bight thereof exteriorly of the tube, allsaid bights being essentially coplanar in a plane parallel with thesurface of the molten glass in said tank, each said bight beinglongitudinally offset from and in overlapping side-by-side relation withthe next adjacent bight, transversely of the ribbon, all said bightsconjointly forming a row extending parallel with and adjacent the lineof draw, and substantially coextensive with the width of the ribbon,said flow control means comprising a multiplicity of valves, each in arespective one of said pipes.
 14. The apparatus of claim 6, said firstcooler means comprising a first multiplicity of discrete U-shapedchambers, means mounting said chambers in side-by-side contiguousrelation, each in a respective oNe of a multiplicity of parallel planesnormal to the line of draw, to form a row extending parallel with andadjacent said line of draw and essentially coextensive therewith, saidfirst conduit means comprising a first header and a multiplicity offirst pipes each connecting said first header with a respective one ofsaid chambers, a multiplicity of valves each in a respective one of saidfirst pipes, and means for exhausting fluid from each chamber of saidfirst multiplicity.
 15. The apparatus of claim 14, said first coolermeans also comprising a second multiplicity of discrete U-shapedchambers, each of said second chambers fitting between the sides of arespective one of said first chambers, to extend in a second rowparallel with, adjacent, and substantially coextensive with the line ofdraw, a second header, a multiplicity of second pipes each connectingsaid second header with a respective one of said second multiplicity ofchambers, and means for exhausting fluid from each of said secondmultiplicity of chambers.